A friction member for a vehicle brake assembly is formed by affixing friction material manufactured from a raw material mixture of fiber, filler and a binder to a steel back plate. However, simply attaching the friction material to just one side of the back plate does not provide the friction member with adequate adhesive strength. As a result, one or more bonding through-holes are formed in the back plate and the friction material is forced into the bonding through-holes at the same time as friction material is affixed to one side of the back plate, in order to increase the strength of the attachment by contacting the friction material against the insides of the bonding through-holes.
FIGS. 7A and 7B are diagrams showing a conventional friction member back plate, with FIG. 7A showing a plan view and FIG. 7B showing a lateral cross-sectional view along a line VII—VII. The friction member is used as the disk pad of a disk brake. A back plate 1 shown in the diagram is formed by using a press to stamp automobile sheet metal or machine tool sheet metal to a predetermined shape and simultaneously forming two bonding through-holes 2, 2, in the back plate 1.
After being stamped by the press, the back plate 1 is subjected to an oil-removal process that removes oil from the surface of the back plate 1. The surface is then finished by sand-blasting, after which it is coated with a thermosetting binder in order to increase the strength of the attachment to the friction material.
The raw material of the friction material is, as described above, a mixture of fiber, filler and a binder. The fiber used is either organic fiber, such as cellulose or aramid fibers, metal fiber made from chips of metal or steel, or inorganic fiber such as rock fiber. The filler is there to provide volume and lubrication, in order to obtain stable friction, and may, for example, be barium sulfate, calcium carbonate or graphite. A thermosetting resin, which may be phenol resin or urea resin, is used for the binder, which binds the fiber and filler together.
The raw material of the friction material, once the ingredients have been mixed together, is then weighed to a predetermined weight, put into a metal mold, not shown, compressed, and formed into a semi-finished product. At this point, the friction material, which in principal is formed only by compression, is not baked but in some cases might be heated to a temperature range within which the binder does not react. It should be noted that the friction member of the present invention includes the aforementioned semi-finished product as well.
FIGS. 8A and 8B are diagrams showing the friction material as a semi-finished product provisionally formed as described above, in which FIG. 8A shows a plan view of the semi-finished product and FIG. 8B shows a front view of the semi-finished product. The semi-finished product 3, although shaped like the final product, is not dense, and has a thickness T that is approximately twice that of a thickness t (shown in FIG. 10) of the final product pressed onto the back plate 1 and compressed to a predetermined density. In addition, convex portions 4, 4 corresponding to the bonding through-holes 2,2 described above are formed on the semi-finished product 3. The convex portions 4, 4 are broad at a base but narrow toward a tip to a diameter d1 that is smaller than a diameter D1 (in FIG. 7) of each of the bonding through-holes 2, 2, so that the convex portions 4, 4 can be fitted easily into the bonding through-holes 2, 2.
When the back plate 1 and the semi-finished friction material product 3 are attached to each other as described above, they are sent to the press shown in FIG. 9. The press is a multi-mold type, with a plurality of sets of molds, each formed by an arrangement consisting of a top mold 5 and a corresponding frame mold 6 and a bottom mold 7, all disposed on a single surface.
A vertically traverse space 6a is formed in the frame mold 6, with the bottom mold 7, which in cross-section is identical to the cross-section of the space 6a of the frame mold 6, entering from below the space 6a to form the bottom of the space 6a, in which the semi-finished product 3 is contained. In the event that the semi-finished product 3 is not used, powdered friction raw material is inserted instead. The bottom mold 7 can be raised and lowered within the space 6a. The top mold 5 can be contacted with and separated from the frame mold 6.
A plurality of top molds 5 are mounted at predetermined intervals on a top mold base 15, with a plurality of frame molds 6 corresponding to the top molds 5 mounted on a frame mold base 16, and bottom molds 7, slidably inserted into the frame molds 6, mounted on a bottom mold base 17. The entire assembly is configured so that the top mold base 15 can descend and the bottom mold base 17 can ascend within the frame mold 6.
A plurality of alignment pins 6b for positioning the back plate 1 are provided on a top surface of the frame mold 6. Two projections 8 corresponding to the two bonding through-holes 2 are provided on a bottom surface of the top mold 5. The two projections 8 are cylinders having a height less than a thickness of the back plate 1 and a diameter D2 less than a diameter D1 of the bonding through-holes 2.
The multi-mold construction of the press shown in FIG. 9 greatly improves productivity. Moreover, the top mold 5, frame mold 6 and bottom mold 7 are detachably mounted on the bases 15, 16 and 17, respectively, and thus can be replaced with other molds. Such a configuration makes it possible to switch easily between the manufacture of friction members of various different shapes.
Next, a description is given of a method of manufacturing the friction member using the manufacturing apparatus shown in FIG. 9.
First, as shown in FIG. 9, the semi-finished product 3 is placed on the bottom mold 7 within the frame mold 6, with the back plate 1 placed on the frame mold 6. Where the semi-finished product 3 is not used, powdered friction raw material is placed inside the frame mold 6, with the back plate 1 placed on top of the raw material and the alignment pins 6b aligning the back plate 1. Thereafter, the top mold 5 descends, the two projections 8 enter the two bonding through-holes 2, 2 from above and the back plate 1 is pressed against the frame mold 6. At the same time, the bottom mold 7 ascends and the convex portions 4, 4 corresponding to the bonding through-holes 2, 2, or the powdered friction raw material, as the case may be, enter the bonding through-holes 2, 2, and the back plate 1 and the semi-finished product 3 overlap and are compressed and heated.
FIG. 10 is a diagram showing a state in which the press has completed compression and heating. As shown in the diagram, the friction material semi-finished product 3, in which the binder material has reacted due to the heat, has been compressed and become denser, with a thickness T halved to a new thickness t, to form a friction material 9 of a predetermined thickness that is attached to the back plate 1. Further, the convex portions 4, 4 inside the bonding through-holes 2, 2 are pressed down from the top by the projections 8, 8 formed in the top mold 5 and spread out within the bonding through-holes 2, 2 so as to adhere tightly to the inner walls of the bonding through-holes 2, 2.
FIGS. 11A and 11B are diagrams showing a plan view and a lateral cross-sectional view, respectively, along a line XI—XI of a friction member formed according to the present invention. A friction material 9 is bonded both to a bottom surface of the back plate and inside surface of the bonding through-holes 2, 2, and increase the strengh of the attachment.
However, in the conventional art described above, the diameter D2 of the cylindrical projections 8, 8 on the top mold 5 must be substantially smaller than the diameter D1 of the bonding through-holes 2, 2. In other words, because of the multi-mold construction of the press as described above, cumulative error occurs when mounting a plurality of molds, and as a result the accuracy with which the projections 8, 8 and the bonding through-holes 2, 2 are aligned cannot be improved. As the diameter D2 of the projections 8, 8 approaches the diameter D1, the projections 8, 8 become unable to enter the bonding through-holes 2, 2 and instead sink into the peripheral areas thereof, which in turn makes separation after formation difficult.
As a multi-mold technique, a method that is described in Japanese Laid-Open Patent Publication No. 2000-27914 is known. This method involves arranging an even number of back plates symmetrically about a line in a single integrated back plate assemblage, pressing a similar integrated assemblage of friction material onto the back plate assemblage, and then cutting into a plurality of friction members.
However, the above-described method handles the back plate as an assemblage of multiple back plates formed into a single integrated structure, and therefore the problem of back plate relative positional error does not arise. Accordingly, no mention is made of the problem of the projections 8, 8 becoming unable to enter the bonding through-holes 2, 2 and instead sinking into the peripheral areas thereof and making separation after formation difficult when affixing friction material to a plurality of back plates.